Bandsawmill not straight entering and leaving

Cruiser_79 · July 22, 2020, 08:43:47 AM

I noticed that my bandsaw creeps up a little in the first 10" of my cut, and loweres just before leaving the cut. My frame is levelled exact, and my sawhead travels level as well. I checked it with a total station and there is at most 1mm of difference in the entire travel of the sawhead. It looks like it get worse with hard, thick logs. I tried to cut a few beams of hardwood and the difference is getting more. Should I level the wheels or is there something else going wrong? Blade is brand new so I would think that's not the problem. With an older blade I had same problem, but less because I was only cutting some pine. I enclosed pictures as well.

Crusarius · July 22, 2020, 08:46:26 AM

if the blade is not parallel to the bed that will cause that. You will probably have to adjust the blade rollers / guides.

Cruiser_79 · July 22, 2020, 11:59:55 AM

Okay thanks, should have thought of that myself :

I adjusted the blade guides a little and made a big difference, but still a little bit of creeping up, but leaving the cut is straight now.
Found out that the axle of the driven wheel isn't exactly level as well, so the wheel isn't parallel to the bed. First fix that as well.

KenMac · July 22, 2020, 02:02:15 PM

Quote from: Cruiser_79 on July 22, 2020, 11:59:55 AM
Okay thanks, should have thought of that myself : I adjusted the blade guides a little and made a big difference, but still a little bit of creeping up, but leaving the cut is straight now.
Found out that the axle of the driven wheel isn't exactly level as well, so the wheel isn't parallel to the bed. First fix that as well.

What mill do you have? Some mills need the wheels slightly off plumb for best results. Check your manufacturer's specs for correct info on alignment issues. Good luck!

esteadle · July 22, 2020, 04:17:58 PM

A sharp sawblade will cut the roundness off of a cant like the one in your picture. A dull sawblade will ride over the top and conform to the shape of the cant if it's not sharp enough.

Look closely at your blades and check them for sharpness. Get a magnifying glass out if necessary. There should be no shininess to the tips at all. They should be completely dull and reflect no light. Look especially closely at the outside edges of the teeth and see if they have been rounded over. Get them sharpened or switch to a nice new blade and you should be able to resolve this issue.

Best of luck to you,

Eric

Cruiser_79 · July 22, 2020, 04:18:06 PM

Quote from: KenMac on July 22, 2020, 02:02:15 PM
Quote from: Cruiser_79 on July 22, 2020, 11:59:55 AM
Okay thanks, should have thought of that myself : I adjusted the blade guides a little and made a big difference, but still a little bit of creeping up, but leaving the cut is straight now.
Found out that the axle of the driven wheel isn't exactly level as well, so the wheel isn't parallel to the bed. First fix that as well.
What mill do you have? Some mills need the wheels slightly off plumb for best results. Check your manufacturer's specs for correct info on alignment issues. Good luck!

It's a Mebor, year 2002. It's Slovenian made and I can't find documentation about it. But one wheel is straight, the driven one is slightly off plumb. There aren't many similar mills around so it's hard to compare. All trial and error at the moment 😅

Cruiser_79 · July 22, 2020, 04:22:48 PM

Quote from: esteadle on July 22, 2020, 04:17:58 PM
A sharp sawblade will cut the roundness off of a cant like the one in your picture. A dull sawblade will ride over the top and conform to the shape of the cant if it's not sharp enough.

Look closely at your blades and check them for sharpness. Get a magnifying glass out if necessary. There should be no shininess to the tips at all. They should be completely dull and reflect no light. Look especially closely at the outside edges of the teeth and see if they have been rounded over. Get them sharpened or switch to a nice new blade and you should be able to resolve this issue.

Best of luck to you,

Eric

I will check the blade tomorrow, but it must be quite okay cause it's brand new, the plastic cover was still around the teeth. I understand what you say about the dull blade riding over top, could it be that the blade is doing this when there is not enough tension? I have 40-60 bar on the meter because that range is marked but not sure or that's too much or too little.

ladylake · July 22, 2020, 04:36:36 PM

What gets me is how does the blade know when the end of the log is coming, do you slow down or speed up at the end. Steve

Chuck White · July 22, 2020, 09:54:28 PM

Steve, I think what it boils down to is that there is somewhat less tension in the log at the ends, and the blade will go where it can go the easiest!

Not positive (of course) but that's what I've always thought, and the blade needs to be sharp in order for you to make it go where you want it to go!

Cruiser_79 · July 23, 2020, 12:40:13 AM

Quote from: ladylake on July 22, 2020, 04:36:36 PM
What gets me is how does the blade know when the end of the log is coming, do you slow down or speed up at the end. Steve

That's interesting indeed. I can see that when the blade leaves the cut it goes down a fraction. I try to keep the speed consistent all the cut, only slowing down a bit when it is getting tough. But in that case I don't speed up anymore.
Can it has to do something with the water I use for cooling/lubrication? Too much or too less? I made a drip hose right above the teeth to cool and lubricate. Just before the blade guides I made a felt which is soaked by a chainoil/diesel mix. And there is a felt against the driven wheel to lubricate the wheel.
This is the water hose with small nozzle.
Behind the blade guide you can see the bolt of the felt holder for oil/diesel, and to sweep some dust of the blade.

PS; this blade is sticky because I sawed some pine dry. That's why I made the diesel hose. The blade that's on the mill now is new and clean.

terrifictimbersllc · July 23, 2020, 05:04:28 AM

If logs are older and off the ground the ends of the log can be drier and harder than the middle of the log.

One would think new blades are sharp and they usually are. But not always as sharp as when resharpened. In fact, there are some here that will sharpen new blades before using them.

Eastedle is right if there are humps like at the beginning of a log, a sharp blade will often go along cutting those humps right off flat, whereas the same blade that sawed them in the first place will just ride up over. In other words if you put on a fresh blade which cuts those humps right off flat, then the cause or at least some of the cause was that the first blade was not sharp enough.

WDH · July 23, 2020, 06:56:00 AM

When that happens on my mill, the blade is not parallel to the mill bed. When that happens, I have to adjust the blade guide with the blade guide adjustment tool.

Magicman · July 23, 2020, 07:14:17 AM

Quote from: Cruiser_79 on July 22, 2020, 08:43:47 AMBlade is brand new

If that is dirt/sand that I am seeing on the log, your blade was not "brand new" past the first inch of sawing.

Cruiser_79 · July 23, 2020, 08:38:27 AM

Quote from: Magicman on July 23, 2020, 07:14:17 AM
Quote from: Cruiser_79 on July 22, 2020, 08:43:47 AMBlade is brand new
If that is dirt/sand that I am seeing on the log, your blade was not "brand new" past the first inch of sawing.

What you see on the picture is dust from a previous cut. Because of the water it sticks to the log. I cleaned them with a hard brush, but it might be better to clean them by powerwasher! I have a precutter but that won't go deep enough to remove old sand/dirt. The logs are really old, they were pulled out the water. I don't know the English name for those beams, but over here they are used for fastening ships in the harbours and protecting bridges/docks etc.
Tomorrow I will take of this band, check its sharpness and place a sharpened one after.
Thanks for the advice

Magicman · July 23, 2020, 12:20:21 PM

Quote from: Cruiser_79 on July 23, 2020, 08:38:27 AMI have a precutter but that won't go deep enough to remove old sand/dirt. The logs are really old, they were pulled out the water.

If they indeed still have "old sand/dirt" you have a problem. Wind blown and also washed sand is usually embedded in such timbers and any is too much.

Cruiser_79 · July 23, 2020, 12:52:11 PM

Maybe I can mount a blade on the precutter that goes a little deeper. It might help that the beams come from fresh water, not from coastal areas where there's lot of sand and wind.

terrifictimbersllc · July 23, 2020, 03:05:46 PM

I use a general strategy when re-sawing dirty or painted beams.

1) cut the first face about 1/2" deep. If it dulls the blade put on a fresh one.
2) turn the first face toward the blade entry side. Cut this second side off about 1/2" deep.
3) repeat on third face cutting into clean wood.
4) turn to the 4th face. Proceed to cut the beam everything now is cutting into clean wood. If the blade is no longer perfectly sharp than change it and use it on the next beam.

Cruiser_79 · July 23, 2020, 03:40:23 PM

That sounds as a good strategy. I wanted to cut 1" at least for the first cut cause the first inch is quite worn in the years. What kind of blades are you using for the precutter? Mine is only cutting a 1/4" or so. I will make a picture of it when I'm at the mill again.

terrifictimbersllc · July 23, 2020, 04:08:21 PM

My bandsaw has a debarker blade with 1/4" wide carbide teeth. When I am cutting old beams I use it but usually it cannot cut deep, only about 1/16" maybe most of the time, unless the beam is soft from decay. It is not very effective if there are cracks with dirt inside.

Cruiser_79 · July 26, 2020, 12:01:22 PM

I think I found at least one of the problems. I couldn't feel the wear on the flywheel bearings, but one was having a really small vibration. I felt it when I cut really slow through that azobe wood. When removing the wheel I found parts of the bearing everywhere...